Fluid transducer

ABSTRACT

A cam drive mechanism for reciprocating a plurality of pistons in a fluid transducer comprising opposed annular lobed cam surfaces and flat reaction tracks for each piston; a plurality of rolling members positioned between each of said opposed cam surfaces and tracks; and a common retainer spacing said rolling means uniformly around said cam surfaces; with said retainer and tracks adapted so that said rolling means roll between each of said opposed surfaces and tracks with substantially the same angular movement and speed.

United States atent Schottler [4 1 May 2, 1972 s41 FLUID TRANSDUCER 2,973,137 2/l96l Jensen...... ....92/|07 1.900.284 3/1933 Herzmark..... ...4l7/460 [72] In n or- H n y l r. N h Ri e i "1- smsus 10/1963 De 91/480 [73] Assignee: Roller Gear Ltd., Zug, Switzerland Primary Examiner-William L. F reeh [22] Ffled' 1970 Attorney-Hume, Clement, Hume & Lee {21] Appl. No.: 31,314

[57] ABSTRACT -417/538o 92/ 107 A cam drive mechanism for reciprocating a plurality of pistons l Cl s 23/06 in a fluid transducer comprising opposed annular lobed cam Field Search surfaces and flat reaction tracks for each piston; a plurality of 92/52; 417/486488' 52 1; 74/58 60 rolling members positioned between each of said opposed cam surfaces and tracks; and a common retainer spacing said [56] Rmmces cued rolling means uniformly around said cam surfaces; with said retainer and tracks adapted so that said rolling means roll UNITED STATES PATENTS r between each of said opposed surfaces and tracks with subg; ii l f stantially the same angular movement and speed. 1 er 3,482,5 12/1969 Bartolo et al. ..74/60 5 Claims, 8 Drawing Figures 56 52 2 .2; J; .3; e 2 .e 56

ii I 7 Z6 52 w 3' 76 75 \J. 5 39 3A Q ,9 ,f

Q I a I I 9 4 4 3 i Z 54 35k 3 31 Z9 Z2 20 30 .92 .37 2 ?2 z I 72 2 29 76 .7 s z:

I ll 7 V t 7 r 5 I l 52 z? :21

Patented May 2, 1972 3,659,971

3 Sheets 2 Patented May 2, 1972 3 Sheets-Sheet 3 FLUID TRANSDUCER BACKGROUND AND GENERAL DESCRIPTION This invention relates generally to an improved drive mechanism for convening rotary motion into reciprocating motion, and vice versa. More particularly, this invention relates to an improved cam drive mechanism for synchronizing the movements of a plurality of pistons in a fluid transducer.

The type of fluid transducer for which this invention is particularly suited is illustrated in my previous U.S. Pat. No. 3,403,668, issued on Oct. 1, 1968, entitled Fluid Transducer." That patent discloses and claims fluid transducers which incorporate a cam-controlled drive mechanism for converting the rotary motion of an input shaft into the reciprocating motion of a piston, such as in a pump or compressor, or for likewise converting the reciprocating motion of a piston into a rotary motion of an output shaft, such as in an engine or hydraulic motor. The cam-controlled drive mechanism set forth in my earlier patent eliminated the need for piston crank shafts, connecting rods and the like, and increased the efficiency and loading capacity of the fluid transducers. The cam drive mechanisms also permit the transducers to be readily adaptable for operation with variable output and fluid displacement characteristics.

The present invention relates to an improved cam drive mechanism that simplifies the design and synchronization of a fluid transducer having a plurality of closely arranged reciprocating components, such as concentric annular pistons. If such a transducer incorporates cam drive mechanisms formed from pairs of opposed cams with rolling elements therebetween, the planetary motion of the rolling elements must be guided and controlled by bevelled gears or other suitable devices so that the rolling elements maintain the proper position with respect to the opposed cams, Without guiding the motion of the rolling elements there is a danger that the rolling elements may slide into a dead center or stall position between the opposed cam lobes. The incorporation of devices, such as bevel gears to guide the motion of the rolling elements would result in a relatively complicated design for a transducer including a plurality of closely arranged pistons.

Furthermore, if each of the reciprocating pistons in such a transducer is provided with a separate cam-controlled drive mechanism, the transducer must include bevel gears or other suitable devices to synchronize the operation of the various drive mechanisms so as to coordinate the stroke and fluid pressure on each piston and produce a smoothly operating transducer. The devices need for synchronizing the motions of a plurality of cam drive mechanisms also are relatively complicated and cumbersome in transducers incorporating a plurality of close-fitting reciprocating pistons.

The present invention minimizes or eliminates the foregoing problems by providing a multiple-piston transducer with a cam-controlled drive mechanism that has a compact and simple design. In this improved transducer, the problems of guiding the motion of the rolling elements with respect to the opposed cam lobes in the drive mechanisms is eliminated by providing each drive mechanism with a camless reaction disc. Each reaction disc is positioned for engagement with the rolling elements of the drive mechanism and each disc defines circumferential tracks for the rolling elements associated with a plurality of reciprocating pistons. Since the tracks are camless, the rolling elements will roll uniformly along the entire track length and the motion of the rolling elements need not be guided with respect to the reaction disc.

The present cam drive mechanism also synchronizes the motion of a plurality of reciprocating pistons in a simple fashion. Each cam drive mechanism in the transducer incorporates a plurality of rolling means for simultaneously driving a plurality of closely arranged pistons by rolling between a cam surface and an opposed track on an associated reaction disc. The rolling means are mounted in a common rotatable retuiner so that the angular speed of the rolling means driving it plurality of pistons are equalized, Also, the tracks in the reaction disc are adapted to provide the rolling means with effective rolling radii which synchronize the angular movement of the plurality of rolling means in each cam drive mechanism.

Additional objects 1 is features of this invention will become more readily apparent from the following description of exemplary embodiments thereof, taken in conjunction with the accompanying drawings, wherein:

FIG. is a longitudinal sectional view of a pump incorporating the features and advantages of the present invention;

FIG. 2 is a cross-sectional view, taken along the line 2-2 in FIG. 1, showing the common roller retainer incorporated in each cam drive mechanism of the present invention;

FIG. 3 is a cross-sectional view of the pump, taken along the line 3-3 in FIG. 1;

FIG. 4 is a plane developed view of the cam drive mechanisms incorporated in the pump illustrated in FIG. 1;

FIG. 5 is an enlarged sectional view of a portion of the cam drive mechanism of the present invention;

FIG. 6 is an enlarged partial sectional view of the cam drive mechanism as viewed along the line 6-6 in FIG. 5;

FIG. 7 is an enlarged partial sectional view of a modified cam drive mechanism incorporating the features and advantages of the present invention; and

FIG. 8 is an enlarged partial sectional view of the modified cam drive mechanism, as viewed along the line 8-8 in FIG. 7.

EXEMPLARY EMBODIMENTS Referring generally to the drawings, the pump embodying the features and advantages of the present invention is generally indicated by the reference numeral 10. The pump 10 includes a sealed pump housing 11 which is symmetrical about a vertical center line, as illustrated in FIG. 1. An inlet port 12 in the housing 11 permits charging of fluid to flow into the pump 10, and an outlet port 13 provides means for discharging the fluid from the pump 10. Intake and exhaust channels 14 and 15 are arranged in fluid communication with the inlet and outlet ports 12 and 13, respectively, to direct the flow of fluid through the pump 10 during the pumping operation.

As illustrated in FIG. 1, the pump 10 includes an annular cylinder block 16 mounted in the central portion of the housing 11. This block 66 is machined to define a plurality of concentric annular cylinders 17, 18, I9 and 20. Each of these annular cylinders 17-20 is aligned with the longitudinal axis of the housing 11. Each cylinder is also in fluid communication with the intake channel 14, through spring-biased intake check valves 21, and with the exhaust channel 15, through spring-biased exhaust check valves 22. As well-known to those skilled in the art, the check valves 21 and 22 respond to the pressure of the fluid in the pump 10 to permit the fluid to be drawn into the cylinders 17-20, through the valves 21, and then exhausted from the cylinders through the valves 22.

The pump 10 further includes a plurality of annular pistons 27, 28, 29 and 30. As illustrated in FIG. 1, these pistons 27-30 are mounted within the annular cylinders 17-20, respectively, and are adapted for reciprocating movement within the cylinders during the operation of the pump 10. Elastomeric seal rings 31, or other suitable piston ring arrangements, are provided to seal the pistons 27-30 in their respective annular cylinders 17-20.

It is desirable to provide the working face of the annular pistons 27-30 with the same effective area to provide a uniform and continuous flow of fluid from the exhaust outlet 13 during the operation of the pump 10. To accomplish this feature, the pistons 27-30, and their associated cylinders 17-20, are dimensioned to compensate for the differing piston diameters. Thus, the outer cylinders 17 and 18, and the associated outer pistons 27 and 28, are dimensioned to have a relatively small radial width or thickness, and the inner cylinders I9 and 20 and inner pistons 29 and 30 are dimensioned to have a portionately larger radial width or thickness. The reciprocating annular pistons 27-30 will therefore have the same effective working area during the operation of the pump and will apply the same pressure to the fluid being pumped despite the fact that the diameter of the outer pistons 27 and 28 is substantially larger than the diameter of the inner pistons 29, 30.

In order to operate effectively, the above-described pistons 27-30 also must be secured from rotating within the pump housing 11. As illustrated in FIGS. 1 and 3, each of the pistons 27-30 is thus provided with a key 32, and the adjacent portions of the cylinder block 16 are provided with axial keyways 33. The keys 32 and keyways 33 prevent rotational movement of the pistons 27-30, but allow the pistons to slide freely in an axial direction within the housing 11. The keys 32 and keyways 33 are arranged in a uniform circumferential pattern on the pistons 27-30 so that the loads on the keys 32 during the operation of the pump 10, and the resulting forces on the pistons, are uniformly distributed.

The pump 10 in accordance with this invention also includes a central input shaft 40 for driving the pistons 27-30. As illustrated in FIG. l,'the shaft 40 is supported by bearings 39 in the ends of the pump housing 11. The illustrated arrangement of the opposed annular pistons 27-30 assures that the axial forces resulting from the operation of the pump 10 are self-contained. Hence, these bearings 39 will be subjected to substantially no axial load, and can be simple, non-thrust bearings. The shaft 40 extends through a central aperture 38, provided in the cylinder block 16. Snap rings 37 on the shaft 40 engage with the adjacent ends of the block 16 and prevent the block from shifting axially with respect to the shaft 40.

In accordance with this invention, the pump 10 further includes a pair of cam drive mechanisms 50 for transmitting the motion of the input shaft 40 to the pistons 27-30. Each of the cam drive mechanisms 50 are identical in construction, and operate in the same manner to convert the rotary motion of the input shaft 40 into reciprocating motion of at least two of the annular pistons 27-30. Accordingly, only one cam mechanism 50 is described in detail below.

Each of the drive mechanisms 50 includes an annular, multi-lobed cam surface connected to each of a pair of pistons. Thus, the end portions of the outer pistons 27 and 28 are machined to define multi-lobed cam surfaces 52, and the end portions of the inner pistons 29 and are machined to define multi-lobed cam surfaces 54. As best seen in FIG. 4, in the illustrated pump 10, the cam surface 52 defines three uniformly spaced lobes 51, and the cam surface 54 defines three uniformly spaced lobes 53. Due to the three lobes on the cams 52 and 54, each of the pistons 27-30 will travel through three power strokes for every two complete rotations of the input shaft 40.

Also, as illustrated in FIGS. 1 and 4, the amplitudes (a) of the lobes 51 and 53 are equal in length. By this arrangement, the resultant power strokes of the pistons 27-30 will be of equal length during the operation of the pump 10. The equal strokes of the pistons 27-30 will cause uniform displacement of the fluid from the cylinders 17-20 and provide a substantially steady and uniform flow of fluid from the pump 10.

FIGS. 1 and 4 further illustrate the circumferential relationship of the cam surfaces 52 and 54. As shown clearly by the phantom lines in FIG. 4, in this embodiment the earns 52 and 54 are arranged so that the respective lobes 51 and 53 are in radial alignment. This arrangement places the lobes 51 on the cam 52 in radial alignment with the lobes 53 on the cam 54, and similarly places the cam recesses 53A on the cam 54 in radial alignment with the cam recesses 51A on the cam 52.

As illustrated in FIGS. 1 and 2, the drive mechanisms 50 in accordance with this invention incorporate a set of rolling elements in engagement with each of the multi-lobed cams 52 and S4. A first set of rolling elements, comprising a plurality of balls 56, engage with the cam surfaces 52 on the outer pistons 27 and 28, and a second set of rolling elements, comprising a plurality of balls 58, similarly engage with the cam surfaces 54 on the inner pistons 29 and 30. Since the earns 52 and 54 are provided with three lobes in this embodiment, each set of rolling elements includes three balls 56 and S8 to correspond with the number of associated cam lobes.

Both sets of balls 56 and 58 in each of the drive mechanisms 50 are mounted within a common ball retainer 60. As illustrated in FIG. 2, the outer balls 56 are positioned within apertures 61 in the retainer 60 at a large diameter D. The diameter D is selected so that the centers of the balls 56 are arranged in axial alignment with the cams 52 on the outer pistons 27 and 28. In the same manner, the inner balls 58 are arranged in apertures 62 in the retainer 60 at a small diameter d, which places the centers of the balls 58 in axial alignment with the earns 54 on the inner pistons 29 and 30. The apertures 61 and 62 in the retainer 60 are slightly elongated in a radial direction with respect to the diameter of the associated balls 56 and 58. With this arrangement, the apertures 61 and 62 permit the balls 56 and 58 to shift radially and be self-seating within the cam drive mechanism. The circumferential dimension of the apertures 61 and 62 is substantially the same as the diameter of the balls 56 and 58 so that the apertures hold the balls 56 and 58 in a predetermined circumferential position on the retainers 60, within a close tolerance.

The apertures 61 and 62 are uniformly spaced in the retainers 60 so that the three balls 56 are angularly spaced by at the large diameter D, and the three balls 58 are angularly spaced by 120 at the small diameter 4. Moreover, the apertures 61 and 62 are staggered in the retainers 60 so that the balls 56 are uniformly spaced between the balls 58, and vice versa. By such an arrangement, the balls 56 and 58 will cooperate to alternately drive the outer pistons 27, 28 and the inner pistons 29, 30 inwardly to produce power strokes at unifomily spaced time intervals during the operation of the pump 10. The fluid output of the pump 10 will thereby be substantially uniform and continuous.

As shown in FIG. 1, each of the ball retainers 60 is mounted on the input shaft 40 adjacent the ends of a pair of inner and outer pistons 27, 29 and 28, 30. The snap rings 37 on the shaft 40 prevent the retainers 60 from shifting axially inward along the shaft 40. The fit between the shaft 40 and the retainer 60 is sufficiently loose so that the retainers can rotate freely about the shaft during the operation of the pump 10.

Each cam drive mechanism 50 in accordance with this invention further includes a camless reaction disc 70. As illustrated in FIG. 1, a disc 70 is positioned on the shaft 40 adjacent each ball retainer 60. Suitable keys 71 lock the discs 70 from rotating on the shaft 40, and suitable snap rings 72 prevent the discs from sliding outwardly on the shaft. Further, the discs 70 abut against the hub portion of the adjacent ball retainer 60 so that inward shifting of the retainers and discs on the shaft 40 is precluded.

In accordance with this invention, the reaction discs 70 engage with the adjacent sets of rolling balls 56 and 58 maintained in the common ball retainer 60. As shown in FIGS. 1 and 5, each of the discs 70 includes concentric roller tracks 76 and 78 in axial alignment with the balls 56 and 58. By this arrangement the balls 56 and 58 will roll along the reaction disc 70 in the tracks 76 and 78, respectively, while simultaneously rolling along the surface of the opposed cam surfaces 52 and 54 To begin the operation of the pump 10, the input shaft 40 is rotated by an external force (not shown). The rotation of the shaft 40 is transmitted to the reaction discs 70 through the keys 71 so that the discs 70 rotate at the same angular speed as the shaft. The angular movement of the discs 70 in turn causes the balls 56 and 58 to roll between the opposed tracks 76, 78, and the cams 52, 54. The outer balls 56 thereby orbit around the shaft 40, in a planetary fashion, at the large diameter D, and the inner balls 58 likewise orbit about the shaft at the diameter :1.

Since the reaction discs 70 are keyed on the shaft 40 against axial movement, the rolling action of the balls 56 and 58 will cause the pistons 27-30 to reciprocate axially within their respective annular chambers as the balls engage with the lobes 53 and 51 on the cams 52, 54. The pistons 27-30 thereby apply a pumping force to the fluid in the pump cylinders 17-20. Any suitable biasing means (not shown) can be employed to return the pistons 27-30 to their outward positions after the pumping stroke is completed. Since each of the earns 52 and 54 include three cam lobes in the illustrated embodiment, each piston 27-30 will move through three inward pumping strokes for every two revolutions of the input shaft 40.

The use of the reaction disc 70 and the common ball retainer 60 in each of the drive mechanisms 50 greatly simplities the design for multiple piston transducers in accordance with this invention. Since the action between the camless tracks 76 and 78 and the balls 56 and 58 is constant, there is no need to include complicated and expensive bevel gearing or the like to control the positioning of the ball retainer 60, and the balls 56 and 58 with respect to the lobed cams 52 and 54. The positioning of the two sets of balls 56 and 58 in the common ball retainer 60 also simplifies the transducer design by synchronizing the motion of the balls so that the two sets of balls 56 and 58 orbit around the shaft 40, at different diameters d and D, with the same angular speed.

The cam drive mechanisms 50 facilitate the use of the same amplitude a for the lobes 51A and 53A on the earns 52 and 54. The mechanisms 50 thereby drive the associated pistons 27-30 through the same power stroke during the operation of the pump 10. Each piston therefore applies equal pumping pressure to the fluid and will displace an equal volume of fluid.

The use of equal amplitudes a for the cam lobes 51A and 53A create different cam angles for the cams 52 and 54, since the diameters of the cam are different. As clearly illustrated in FIG. 4, the cam angle -y for the small diameter cam 54 is greater than the corresponding cam angle 'y for the large diameter cam 52, when both cams have the same lobe amplitude a. This difference between the angles y, and y, is a function of the difference between the diameters d and D for the earns 54 and 52, respectively.

The existence of the different cam angles and diameters for the cams 52 and 54 inhibits the synchronization of the motion fro the two sets of balls 56 and 58. Since both sets of balls 56 and 58 are in the same retainer 60, their angular speeds will be equal. However, as evident from FIG. 4, the balls 56 and 58 will roll along paths of different circumferential lengths on the associated cams 52 and 54, respectively, for each revolution of the common ball retainer 60, because the cam angles and diameters are different. Thus, there is a natural tendency for one set of balls to slide on the cams and resist the smooth rolling motion of the other set of balls during the operation of the pump 10. The use of the common ball retainer 60 and the different circumferential lengths for the paths of the balls 56 and 58 on the cams 52 and 54 combine to create friction and reaction forces which tend to prevent the proper functioning of the pump 10.

in accordance with this invention the potentially adverse effect of the different circumferential lengths of the earns 52 and 54, and different cam angles y, and 7,, are offset by providing means to correspondingly vary the effective rolling radii for the balls on the adjacent reaction disc 70. Generally, these different rolling radii are produced by recessing the roller tracks 76 and 78 on each disc 70 in a selected manner so that the balls 56 and 58 engage the tracks at selected contact points.

FIGS. 4, 5 and 6 illustrate more specifically the manner in which the tracks 76 and 78 are constructed in accordance with this invention to produce the desired effective rolling radii p. Each track is formed as a V-shaped recess or groove in the interior face of the disc 70. As shown in FIG. 5, the balls 56 and 58 will thereby engage with the sides of the grooved tracks at contact points P. The location of the contact points P with respect to the center C of the balls 56 and 58 is a direct function of the track groove angle a. Hence, the effective rolling radii p for the balls 56, 58 in the grooved tracks 76, 78 is likewise a function of the track groove angle a. As seen in FIG. 5, the effective radii are smaller than the actual radii rfor the balls, and decrease in length as the groove angle a increases. The effective radius p of the balls 56 and 58 therefore depends upon the following geometric relationship between the balls and the track grooves:

( l p r cosa Thus, one of the tracks, such as the outer track 76, can be designed to have a particular groove angle 01,. The selection of the angle a, thereby determines the effective rolling radius p, through which the balls 56 roll along the outer track 76. Then, the groove angle a, for the inner track 78 can be calculated so that the effective rolling radius for the engaged balls 58 will compensate for the different diameters D and d, cam angles 7,, and 7,, and circumferential lengths of the cams 52 and 54.

The relationship between the cam angles 7 and the efiective rolling radii p for the cams 52, 54, and the balls 56, 58 and the groove angle a for the tracks 76, 78 can be described in geometric terms. For purposes of analysis, it is assumed that the ball retainers 60 are held stationary and the opposed cams 52, 54 and tracks 76, 78 are frictionally connected with each other through the rolling balls 56, 58, respectively. Referring to FIGS. 5 and 6, it will be understood that, in general, the angular distance at through which the balls 56, 58 will roll on the cam surfaces 52, 54 in response to an angular movement 6 of the associated disc will be proportionate to the relationship between the ball radium r and the effective radius p for the engaged track 76, 78. Hence, taking into account the fact that the balls 56, 58 roll along the inclined cams 52, 54 having a cam angle 3 (2) w/cos'yr= 8/p Also, since the cams 52, 54 are restrained from rotation and the tracks 76, 78 are on the same rigid disc 70, the following relationships also prevail between the movement of the outer balls 56 at the diameter D and the inner balls 58 at the diameter d along the outer and inner cams 52, 54 and tracks 76, 78:

( l and Also, from equation (2) above it is evident that the angular movement 8,, of the outer grooved track 76, and the angular movement 6, for the inner grooved track 78 can be expressed as follows:

Bi accordance wi tlfthis inventionrthe r5212 grdove angles a (FIG. 5) are selected so that the resultant effective radii p and p, offset the efiect of the different cam angles 7,, and 7, for the earns 52 and 54, respectively, and equalize the effective angular movement of the tracks 76 and 78. Hence, from equations (6) and (7):

be expressed:

( L tan m- K .L "int/6 Since the cam amplitudes a for the cams 52 and 54 are equal, from equations l l) and l 2):

(13) i Dtan -d tan The method of employing the above-described relationships for designing the cam drive mechanisms 50 will be evident from the following example where the radii r, and r, of the balls 56 and 58 are the same; the groove angle 0: for the outer track 76 is selected as 20; D is 84 mm; d is 56 mm; and a is 3.5 mm. From equation l p r cos 20 0.93969r With equation l l =0 075788 7rD/6 1r 84/ 6 Therefore, ,f= A 20', and cos 0.99714. Then from equation l4):

tan "Y0:

l0 tan tam 0.075788 tan-y, 0.11368 Therefore 73/, =6 29 and cos w, 0.99360 Next, from equation 10) above, the effective rolling radius for the balls 58 rolling in the track 78 can be determined:

cos 'y; 0.9939(2 oos 'y 099714 Finally, from equation l cosa, 0.93634 and thus a, 20 33 Therefore, referring to FIG. 5, a groove 76 (2a,) is to be combined with a 41 6 groove 78 (2ai). With such groove angles, the angular speed and movement of the two sets of balls 56 and 58 in the common retainer 60 will be equalized. The balls 56, 58 will therefore roll smoothly, and the friction and reaction forces will be substantially reduced during operation ofthe pump 10.

FIGS. 7 and 8 illustrate a modified cam drive mechanism in which the rolling balls 56, 58 have been replaced by pressure rollers 80, and the angular grooves 76, 78 in the reaction disc 70 have been replaced by modified grooved tracks 90. The rollers 80 are adapted to have stepped surfaces 82 and 84 which define different rolling radii for the rollers with respect to the cams 52, 54 and reaction disc 70. The larger roller surface 82 defines the radius r through which the rollers 80 engage with the cams 52, 54. In the same regard, the smaller rolling surface 84 defines a smaller effective rolling radius p through which the rollers 80 engage the reaction disc 70. The grooved track 90 is dimensioned to receive the larger rolling surface 82 with sufficient clearance so that the surface 82 can freely roll along the disc 70. A modified roller retainer 60A receives the axle pins 81 for each roller 80, and supports a set of rollers 80 in axial alignment with each cam surface 52 and 54.

The modified cam drive mechanism incorporating the rollers 80 can be designed, in accordance with the abovedescribed equations, in a manner similar to the procedure for designing the cam mechanisms 50 including the balls 56 and 58. First, a desired radius (r, and r,) is chosen for the larger 5 roller surfaces 82 on each of the rollers 80. An effective rolling radius p for the smaller roller surface 84 on one of the rollers 80 is also selected, such as the rolling radius p for the outer rollers 80 positioned opposite the cams 52. The diameters D and d, and the cam amplitude a for the earns 52 and 54 will also be known.

From this data, the efiective rolling radius p, for the smaller surface 84 on the set of other rollers 80 on the common retainer A can be calculated. For example, the foregoing data will permit the calculation of the rolling radius p, for the 55 surface 84 on the inner rollers 80 by employing equation (10). Although any desired initial rolling radius p can be chosen to begin the calculations described above, it is expected that the selected radius p, such as the radius p will be chosen to equal the rolling radius r for the rollers 80. By such an arrangement, the steps on one of the sets of rollers in each common retainer 60A will be eliminated, and the design for the cam mechanism thereby simplified. The selection of the effective radius p, to equal r for one of the rollers 80 further simplifies the cam drive mechanism by eliminating the need for the an- 75 nular groove in the reaction disc 70 adjacent that set of rollers.

Although the invention has been described above with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example. Consequently, numerous changes in the detail of construction and in combination of componenm of the transducer, as well as in the possible modes of utilization, will be apparent to those skilled in the art, and may be resorted to without departing from the spirit and scope of the invention.

What is claimed is:

1. A cam drive mechanism for reciprocating a pair of pistons in a fluid transducer comprising:

cam means defining first and second annular cam surfaces each adapted to reciprocate one of said pistons, and having selectively diflerent circumferential lengths;

first and second annular flat reaction tracks spaced in op posed positions adjacent said first and second cam surfaces, respectively;

rolling means positioned between said opposed cam surfaces and reaction tracks; and

roller retaining means engaged with said rolling means and rotatable to orbit said rolling means between said opposed cam surfaces and tracks at a common angular speed;

said rolling means engaging each cam surface at a selected cam rolling radius and each reaction track at a selected track rolling radius as said rolling means orbit therebetween; and

said opposed cam surfaces and tracks being arranged to define effective cam and track rolling radii which compensate for the different circumferential lengths of said cam surfaces and cause said rolling means to roll freely in engagement between said opposed first and second cam surfaces and tracks with substantially the same angular movement and speed, to thereby substantially reduce reaction and friction losses in said drive mechanism.

2. A cam drive mechanism in accordance with claim I wherein said first and second cam surfaces are concentrically positioned and include a plurality of uniformly spaced cam lobes of equal lobe amplitude.

3. A cam drive mechanism for reciprocating a plurality of pistons in a fluid transducer comprising:

first and second annular an concentric cam members each adopted to reciprocate one of said pistons, said cam members having different selected diameters and including a plurality of uniformly spaced cam lobes having substantially the same lobe amplitude and selectively different cam angles;

first and second reaction tracks comprising annular and concentric grooves spaced in opposed positions adjacent said first and second cam members, respectively;

a plurality of rolling balls positioned between said opposed cam members and reaction tracks and uniformly spaced with respect to said cam lobes, said rolling balls engaging each cam member at a selected cam rolling radius and each reaction track at a selected track rolling radius as said balls orbit therebetween;

said cam and track rolling radii being selected so that said balls roll freely along said first and second tracks with the same angular movement; and

roller retaining means engaged with said balls and rotatable between said opposed cam members and tracks to orbit said balls therebetween at a common angular speed.

4. A cam drive mechanism for reciprocating a plurality of pistons in a fluid transducer comprising:

first and second annular and concentric cam members each adopted to reciprocate one of said pistons, said cam members having different selected diameters and including a plurality of uniformly spaced cam lobes having substantially the same lobe amplitude and selectively different cam angles;

first and second reaction tracks comprising annular and concentric grooves spaced in opposed positions adjacent said first and second cam members, respectively;

a plurality of multi-step rollers positioned between said opposed cam members and reaction tracks and uniformly spaced with respect to said cam lobes, said rollers having an outer surface engaging each cam member at a selected cam rolling radius and an inner surface engaging each reaction track at a selected track rolling radius within one of said grooves as said rollers orbit between said opposed cams and tracks;

said cam and track rolling radii being selected so that said rollers roll freely along said first and second tracks with the same angular movement; and

roller retaining means engaged with said rollers and rotatable between said opposed cam members and tracks to orbit said rollers therebetween at a common angular speed.

5. A cam drive mechanism for reciprocating a plurality of pistons in a fluid transducer comprising:

first and second annular cam members each adapted to reciprocate one of said pistons, said cam members including cam lobes having selectively different cam angles 7i and 72 respectively;

first and second annular reaction tracks spaced in opposed positions adjacent said first and second cam members. respectively;

rolling means positioned between said opposed cam members and reaction tracks and engaging said first and second cam members at selected rolling radii r, and r respectively and further engaging said first and second reaction tracks at selected track rolling radii pi and p2 respectively, as said rolling means orbit between said opposed cam members and tracks; and

retaining means engaged with said rolling means and rotatable between said opposed cam members and tracks;

said track rolling radii for said rolling means being selected in accordance with the relationship so that said rolling means orbit at substantially the same angular speed and roll freely along said first and second reaction tracks with substantially the same angular movement.

* I! i i i 

1. A cam drive mechanism for reciprocating a pair of pistons in a fluid transducer comprising: cam means defining first and second annular cam surfaces each adapted to reciprocate one of said pistons, and having selectively different circumferential lengths; first and second annular flat reaction tracks spaced in opposed positions adjacent said first and second cam surfaces, respectively; rolling means positioned between said opposed cam surfaces and reaction tracks; and roller retaining means engaged with said rolling means and rotatable to orbit said rolling means between said opposed cam surfaces and tracks at a common angular speed; said rolling means engaging each cam surface at a selected cam rolling radius and each reaction track at a selected track rolling radius as said rolling means orbit therebetween; and said opposed cam surfaces and tracks being arranged to define effective cam and track rolling radii which compensate for the different circumferential lengths of said cam surfaces and cause said rolling means to roll freely in engagement between said opposed first and second cam surfaces and tracks with substantially the same angular movement and speed, to thereby substantially reduce reaction and friction losses in said drive mechanism.
 2. A cam drive mechanism in accordance with claim 1 wherein said first and second cam surfaces are concentrically positioned and include a plurality of uniformly spaced cam lobes of equal lobe amplitude.
 3. A cam drive mechanism for reciprocating a plurality of pistons in a fluid transducer comprising: first and second annular an concentric cam members each adopted to reciprocate one of said pistons, said cam members having different selected diameters and including a plurality of uniformly spaced cam lobes having substantially the same lobe amplitude and selectively different cam angles; first and second reaction tracks comprising annular and concentric grooves spaced in opposed positions adjacent said first and second cam members, respectively; a plurality of rolling balls positioned between said opposed cam members and reaction tracks and uniformly spaced with respect to said cam lobes, said rolling balls engaging each cam member at a selected cam rolling radius and each reaction track at a selected track rolling radius as said balls orbit therebetween; said cam and track rolling radii being selected so that said balls roll freely along said first and second tracks with the same angular movement; and roller retaining means engaged with said balls and rotatable between said opposed cam members and tracks to orbit said balls therebetween at a common angular speed.
 4. A cam drive mechanism for reciprocating a plurality of pistons in a fluid transducer comprising: first and second annular and concentric cam members each adopted to reciprocate one of said pistons, said cam members having different selected diameters and including a plurality of uniformly spaced cam lobes having substantially the same lobe amplitude and selectively different cam angles; first and second reaction tracks comprising annular and concentric grooves spaced in opposed positions adjacent said first and second cam members, respectively; a plurality of multi-step rollers positioned between said opposed cam members and reaction tracks and uniformly spaced with respect to said cam lobes, said rollers having an outer surface engaging each cam member at a selected cam rolling radius and an inner surface engaging each reaction track at a selected track rolling radius within one of said grooves as said rollers orbit between said opposed cams and tracks; said cam and track rolling radii being selected so that said rollers roll freely along said first and second tracks with the same angular movement; and roller retaining means engaged with said rollers and rotatable between said opposed cam members and tracks to orbit said rollers therebetween at a common angular speed.
 5. A cam drive mechanism for reciprocating a plurality of pistons in a fluid transducer comprising: first and second annular cam members each adapted to reciprocate one of said pistons, said cam members including cam lobes having selectively different cam angles gamma i , and gamma 2 , respectively; first and second annular reaction tracks spaced in opposed positions adjacent said first and second cam members, respectively; rolling means positioned between said opposed cam members and reaction tracks and engaging said first and second cam members at selected rolling radii r1 and r2, respectively and further engaging said first and second reaction tracks at selected track rolling radii Rho i , and Rho 2 , respectively, as said rolling means orbit between said opposed cam members and tracks; and retaining means engaged with said rolling means and rotatable between said opposed cam members and tracks; said track rolling radii for said rolling means being selected in accordance with the relationship so that said rolling means orbit at substantially the same angular speed and roll freely along said first and second reaction tracks with substantially the same angular movement. 